This is how support material should work: Easy enough to peel, but sticky enough to hold the part in place while printing.
And this is how multi-material prints should work out: UV-resistant material up top, grippy rubber on the bottom, all welded together for eternity. These are surprisingly easy to get right if you keep a couple of tricks in mind and use the right material combinations. So buckle up as we go through what works, what doesn’t and how you can improve things.
This is one of the things that I’ve wanted to test out ever since I got my hands on the five-head Prusa XL. Multi-color is nice, but for functional parts, I want to be able to mix either materials with different properties or get total design freedom by having support material that a) doesn’t require hours of peeling and b) leaves a surface that is smooth, scar-free and geometrically accurate.
So, I needed a way to test material adhesion, and this is what I came up with.
It’s designed as two separate bodies that have zero clearance between each other. The first section has a 20mm supported bridge to check how easily a block of support material will break out without damaging the supported part. Then, a 13mm flat area with just one side anchored to the main material, what I’ve seen before with materials that only barely stuck to each other was that structures like this would start peeling and warping up, so I’m trying to see which combinations would show that behavior here. Finally, a 15mm sphere that is completely embedded in the bottom material, to check surface finish and separability.
A neat little trick that I used here to save me a whole bunch of clicking in the slicer is that I used tiny bars to fuse each full row of the bottom parts and each full column of the top parts into their own body so that I’d only have 10 bodies total in the slicer and could easily select them as whole rows and columns.
I would print these from PLA, PETG, ABS, ASA, and a flexible material, which should cover almost all the bases. I thought about also including a PA or Nylon material instead of ABS but decided against it because Nylons are pretty rarely used, they require their own set of printing parameters that would in turn make everything else harder to print, and they also tend to not stick well to really anything from the start.
The materials I used initially are PLA and PETG from VoxelPLA, some random, old ABS that would turn out to be too past its prime, so I’m not going to shame them here, Prusament ASA, as well as Fiberlogy Fiberflex 40D. And as I alluded to, the first print didn’t go particularly well. I used the smooth PEI-coated bed, set to 100°C throughout the print, and had the enclosure closed, but the ABS bits still came loose from the bed and ruined the entire print. On the other hand, the flexible parts were super hard to remove, they do come off without visibly damaging the bed, but they do require an uncomfortable amount of force.
But this was pretty much what I expected, so I switched it up a little, used the textured PEI-coated bed, and instead of the ABS, I loaded an extra type of Flex, Polymaker’s Polyflex. Flexible materials have a lot more variance in what exact material they are, so I expected an interesting difference in how well they would bond to other materials, too. But the problem is that the Polyflex filament itself has a much grippier surface than the Fiberflex, and it immediately jammed in the XL’s extruder. I do like the grippy properties of Polyflex, but it would need more tuning and probably very slow print speeds to get parts out reliably.
And then I remembered: I already had a perfectly good spool of ABS that I had just extruded myself on the 3Devo machines, which was fresh and made from good material – Polylac 747S to be exact. I loaded that up, and this time, to make sure the parts would stick, I coated the entire textured bed in a nice, even layer of glue stick. That’s messy, but it’s one of the few solutions that sticks to almost all filaments equally well, but most importantly, allows flexibles to release without ripping the printed part in half. And this worked! Surprisingly, it looked like all the different materials stuck together well enough during the print with no warping – no doubt having an enclosure helped here, especially with ABS and ASA.
PLA as bottom
Starting with PLA as the bottom or support material, PETG on top is very easily peelable and leaves a nice surface finish, the bridge, toilet bowl and sphere came apart perfectly. ABS and ASA are similar, with ASA maybe sticking marginally better, but in either case, they’re easily separable and leave perfect surface finished. Flex stuck noticeably better than the other materials when printed onto PLA, but because it’s flexible and PLA is very rigid, it’s still nicely peelable.
So far, PLA has done a great job as a support material but isn’t very good for permanently combining with other materials.
PETG as bottom
Then, PETG on the bottom. PLA separates well, but now ABS and ASA start welding really well to the PETG base. It’s not a total, 100% weld, these are still dissimilar plastics after all, but enough to permanently tack the two materials together if they’re not going to see huge mechanical loads. Trying to separate them had me damaging or destroying half of the part, so it’s not a good combination for support materials. Finally, Flex welded itself to the PETG completely, making it a good combination for adding hinges, seals, or grippy bits to a part.
ABS and ASA as bottom
ABS and ASA performed the exact same as base materials, so I’m going to group them as one, they are chemically pretty closely related after all. PLA printed on top was reasonably easy to separate, while PETG welded itself to the base material, but this time, the bond was noticeably weaker than printed the other way around where I had PETG as the base and ABS or ASA on top. With PETG on top, the bond is a bit too weak to be totally mechanically reliable, but too strong to be useful as a support material, so not much use there. ABS stuck perfectly to ASA and vice-versa, not much of a surprise there, and Flex stuck very well to both filaments. You can still peel it off if you really rip on it, but in practice, this is a permanent bond.
Flex as bottom
Flex as the base material would make a fantastic support material for PLA because you can nicely peel it off. I know that using flex as support material might sound excessive, but if you use it just for the interface layers, it could be worth trying for tricky parts. PETG bonds extremely well when printed onto Flex, and ABS and ASA functionally bond themselves to Flex as well, but going the other way around with Flex on top of ABS or ASA did provide a little bit of a better grip.
Conclusion
First of all, printing materials on top or bottom makes some difference, but not enough where it matters a whole lot. In general, printing the higher-temperature material on top tends to fuse a little better.
PLA doesn’t really stick to anything other than itself, and not even flexibles stick to it, so it makes for a great support material and is probably the only material worth using as one if you want to print supports with zero clearance like I did.
PETG sticks surprisingly well to everything but PLA. It creates an inseparable weld with flexibles, but if you have a particularly tricky part to support and can’t use zero-clearance PLA as support, or PETG for a PLA part, for example with ASA, you could still get a benefit from using PETG supports with regular clearance instead of printing everything out of the same material.
Tips and Tricks
Tree supports in PrusaSlicer are a bit weird. When they work, they’re fantastic, but I often got these shifts in the alignment of the main tree trunks, they usually print okay-ish, but sometimes they don’t, and also, the way the interface for tree supports is generated seems to ignore any clearance settings you make, so the only way to get zero-clearance supports is to use the classic, straight support material columns. I did make these as lightweight as possible, by setting the spacing to 6mm and using honeycomb so they don’t fall over. Then I used 7 solid interface layers on top, though a little less than that would have worked as well and would have made peeling easier. In any case, top contact Z distance, Interface pattern spacing, and XY separation are all set to 0 to get that perfect molded look.
I also overestimated how well overhangs would print, so on the inside here, I now have a perfectly printed area where the overhang isn’t very steep, then a section where the perimeters drooped, and then another perfect section where I had the zero-gap support material. Using a smaller layer height would have helped with the overhangs, but for 0.25mm layers, just be more conservative and generate more support material.
When you are using two different filaments for your part and support, try to use the same color for both, or at least use clear for the support material. I used teal PETG on white PLA because it looks good on video, and while it came off pretty cleanly, there are still some tiny teal spots on the main part.
Finally, a tip for removing PLA supports: Use a bit of heat! PLA easily softens under warm to hot water, while the PETG or ASA print itself will stay rigid much longer, and that makes peeling out stubborn PLA supports just a bit easier.
One of the challenges with printing all these different materials in one go was bed adhesion. They work best on different surfaces and surface temperatures, and the slicer notifies you about that. PLA will start warping if it’s printed at too high of a bed or ambient temperature, but it’s not the end of the world. I have yet to figure out what bed temperatures PrusaSlicer uses when you have got different materials loaded up. But to make sure it has no chance but to use ones that will stick, I created a new material profile for each filament with all equal bed temperatures that will work for all filaments I’m using at the same time. An enclosure or using a sticky coating like glue stick will allow you to use slightly lower bed temperatures that will keep all the filaments in a more happy place.
What you can also do for support material is to use the peelable material just for the interface, so that the largest part of the support structure is printed at the settings the material wants to be printed at.
And lastly, getting materials to stick together better. You can, of course, design them already keyed together in CAD, but the PrusaSlicer 2.9 beta just added better fuzzy skin and fuzzy skin painting. So painting just the contact surface with fuzzy skin is going to create a little more overlap between the segments of the parts and should bond them together more thoroughly.
I actually noticed this with the Cubone skull where I had fuzzy skin enabled for the entire print, and even the PETG support material on the PLA print was a bit harder to remove than I expected. Support material gets generated for the “ideal” surface, not for the fuzzy one, so these did end up keying together a little more than I expected.
So I hope this was helpful, as always, thank you for watching, keep on making and I’ll see you in the next one.
Models shown: Cubone Dog Mask by aolesin
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